This invention relates to a digital indicator device for displaying the Apex indication exposure values. The indicator is adapted to provide an indication of every step and fractions of a step.
The Apex indication values are related to one another by the well known Apex indication equation: EQU E.sub.v = B.sub.v + S.sub.v = A.sub.v + T.sub.v, (1)
where;
B.sub.v is the Apex indication value of brightness; PA1 S.sub.v is the Apex indication value of film sensitivity; PA1 A.sub.v is the Apex indication value of aperture opening; PA1 T.sub.v is the Apex indication value of shutter speed; and PA1 E.sub.v is the Apex indication exposure value.
It is quite common for cameras to display the A.sub.v or T.sub.v values by means of a meter. Such a display is an analog indication of these values. It is less common but also known to display the E.sub.v values by a meter. More recently, digital display devices have been used to digitally indicate to the camera user, the values A.sub.v, T.sub.v and/or E.sub.v. While such displays are very useful, they do have the disadvantage of not being capable of indicating values intermediate two nominal values.
Some such systems use one step for every .+-. 1 E.sub.v, A.sub.v or T.sub.v, and therefore are not high precision systems, whereas in other systems, in which illuminant members (electric lamps or the like) are aligned along the frame of a finder field to read numerical values on a character plate fixedly mounted corresponding in position to illuminant members, precise indication is not possible because digital readout is not provided.
In the Kisanuki U.S. Pat. No. 3,909,137, a very complex system, using analog to digital converters with digital to analog feedback, is described for providing a digital indication of the steps of a specific combination of Apex indication values plus an indication of fractional parts of one step of the specific combination of values. The value specifically displayed in the Kisanuki patent is the value B.sub.v -T.sub.v, which the patent refers to generally as the exposure value. However, the "exposure value" of the Kisanuki patent is not the exposure value E.sub.v which equals B.sub.v + S.sub.v and A.sub.v + T.sub.v.